Prophetic Commentary on the Qur'an (Tafseer of the Prophet
(pbuh))

Bukhari :: Book 6 :: Volume 60 :: Hadith 190

Narrated Abu Musud:

When we were ordered to give alms, we began to work as porters
(to earn something we could give in charity). Abu Uqail came with
one half of a Sa (special measure for food grains) and another
person brought more than he did. So the hypocrites said, "Allah is
not in need of the alms of this (i.e. 'Uqail); and this other
person did not give alms but for showing off." Then Allah
revealed:--

'Those who criticize such of the Believers who give charity
voluntarily and those who could not find to give in charity except
what is available to them.' (9.79)